Front and rear curtain shutter device with start area

ABSTRACT

A shutter device includes a stationary plate having a plurality of driving electrodes movable element opposes the stationary plate and including a sheet subjected to an electret-forming process. A drive control unit for moving the movable element using variation in electrostatic force, thereby shielding light. The electrostatic force is generated between constant charges held in the movable element as a result of the electret-forming process, and charges generated in each of the driving electrodes when a voltage is applied to each driving electrode. The generated electrostatic force is varied by varying the voltage applied to each driving electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 10/965,149, filed Oct, 14, 2004, now U.S. Pat. No. 7,182,530, whichis based upon and claims the benefit of priority from prior JapanesePatent Application No. 2003-355460, filed Oct. 15, 2003, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a shutter device.

2. Description of the Related Art

Various mechanisms for acquiring a compact shutter device of a simplestructure for use in, for example, cameras have been proposed so far.For example, the shutter mechanism disclosed in Jpn. Pat. Appln. KOKAIPublication No. 8-220592 comprises a stationary element having beltlikeelectrodes arranged with a predetermined pitch and a light-passingopening, and a movable element provided movable to the stationaryelement for shielding the opening from light or permitting light to passtherethrough, the movable element having a resistor layer opposing theelectrodes of the stationary element. The shutter mechanism furthercomprises a drive control section for varying the voltage applied to theelectrodes of the stationary element. In other words, this shuttermechanism is an induction electrostatic actuator. The shutter mechanismcontrols the movement of the movable element to control thelight-passing time or area of the opening. This structure enables themovable element as a shutter curtain to be directly controlled. As aresult, the opening/closure of the shutter can be accurately controlledby a simple mechanism.

BRIEF SUMMARY OF THE INVENTION

The present invention aims to provide a shutter device capable ofdriving a shutter at a high speed with a low voltage.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may beleaned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and together with the general description given above and the detaileddescription of the embodiment given below, serve to explain theprinciples of the invention.

FIG. 1 is a schematic view illustrating a shutter device according to afirst embodiment of the invention;

FIGS. 2A and 2B are views useful in explaining the open/close operationsof the shutter device;

FIGS. 3A to 3C are sectional views useful in explaining movable elementsof different structures;

FIG. 4 is a sectional view illustrating an example of a sheet subjectedto an electret-forming process, which forms the movable element;

FIG. 5 is a sectional view useful in explaining the structure of astationary plate;

FIGS. 6A to 6D are views useful in explaining the operation principle ofthe movable element;

FIG. 7 is a graph illustrating an example pattern of a voltage appliedto a driving electrode by a drive control circuit;

FIGS. 8A to 8C are views illustrating modifications of the drivingelectrode;

FIG. 9 is a flowchart illustrating the procedure of control performed inthe drive control circuit upon turn on;

FIGS. 10A and 10B are views illustrating a case where a capacitancesensing circuit is connected to the driving electrode;

FIG. 11 is a view illustrating a structural example in which the movableelement is sealed; and

FIG. 12 is a view illustrating the structure of a focal plane shutterdevice according to a second embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described in detail with referenceto the accompanying drawings.

First Embodiment

FIG. 1 is a schematic view illustrating a shutter device 100 accordingto a first embodiment of the invention. As shown, the shutter device 100includes a stationary plate 1, movable element 4, and drive controlcircuit 3. The stationary plate 1 is provided with a plurality ofbeltlike driving electrodes 2 arranged at regular intervals, and anopening 5 for passing therethrough light that enters the shutter device100. The movable element 4 is a sheet member opposing the stationaryplate 1. The drive control circuit 3 applies an alternating voltage tothe driving electrodes 2. The movable element 4 is subjected to anelectret-forming process. The electret-forming process means a processfor making a dielectric kept in a permanently electrically polarizedstate to hold a constant charge. The driving electrodes 2 extend in adirection perpendicular to the movement direction (the side-to-sidedirection in the figure) of the movable element 4.

In the shutter device 100 shown in FIG. 1, when a voltage is applied tothe driving electrodes 2, the driving electrodes are charged withelectricity. At this time, an electrostatic force is exerted between thecharge generated in each driving electrode and the constant charge heldin the movable element 4. The electrostatic force therebetween is variedby varying the voltage applied to each driving electrode, thereby movingthe movable element 4. In the case of FIG. 1, the driving electrodes 2are provided almost all over the stationary plate 1 except for the areaof the opening 5. Since the total area of the driving electrodes 2 onthe plate 1 is thus made maximum, the force for driving the movableelement 4 is maximized.

Although the opening 5 is square in FIG. 1, the opening can also bemade, for example, circular, of course. Further, in the firstembodiment, the opening 5 is formed in the stationary plate 1. However,the opening 5 may not always be formed in the plate 1. For instance,light may be passed through a portion other than the stationary plate 1,or the stationary plate 1 and driving electrodes 2 may be formed of alight transmissible material. In these cases, the driving electrodes 2can be provided almost all over the stationary plate 1.

FIGS. 2A and 2B are views useful in explaining the open/close operationsof the shutter device shown in FIG. 1. Specifically, FIG. 2A shows astate in which the opening 5 is exposed, i.e., the shutter is open. Inthis state, the light entering the shutter device 100 passes through theopening 5. FIG. 2B shows a state in which the opening 5 is shielded withthe movable element 4, i.e., the shutter is closed.

Referring then to FIGS. 3A to 3C and 4, the movable element 4 will bedescribed. FIG. 3A is a sectional view illustrating an example of themovable element 4 shown in FIG. 1. The movable element 4 shown in FIG.3A is formed of a sheet 41 subjected to an electret-forming process(hereinafter referred to simply as “the sheet 41”), and a metal sheet 42as a light shield stacked thereon. The sheet 41 may be formed of, forexample, fluoroethylene propylene (FEP). The FEP sheet is subjected to,for example, corona discharge for converting the sheet into anelectret-formed one.

The stacking of the metal sheet 42 on the sheet 41 significantly reducesthe light transmittance of the movable element 4. Further, this processcan reduce the entire thickness of the movable element 4 to aboutseveral micrometers. As a result, the movable element 4 can be reducedin weight. The thinner the sheet 41, the higher the charging efficiencyin the electret-forming process. As a result, the movable element 4 canhave a high charge density. The sheet 42 is not limited to a metalsheet. It is sufficient if the sheet 42 has high light-shieldingproperties.

FIG. 3B shows another example of the movable element 4. The movableelement 4 shown in FIG. 3B is formed of the sheet 41 subjected to anelectret-forming process, a metal sheet 42, and a sheet 43 as alight-absorbing member with a light transmittance of about 1 to 5%(hereinafter referred to simply as “the sheet 43”). These sheets arestacked on each other. The sheet 43 is formed by, for example, coating adielectric sheet with black paint.

The stacking of the metal sheet 42 and the sheet 43 on the sheet 41significantly reduces the light transmittance of the movable element 4,and prevents light from being diffusedly reflected from the metal sheet42. As a result, a light movable element 4 of satisfactorylight-shielding properties can be provided. Further, since the sheet 43can prevent diffused reflection of light, if the shutter device of theembodiment is used in, for example, a camera, the quality of photographyis enhanced.

FIG. 3C shows yet another example of the movable element 4. The movableelement 4 shown in FIG. 3C is formed of the sheet 41 subjected to anelectret-forming process, and a sheet 44 (hereinafter referred to simplyas “the sheet 44”) formed of, for example, plastic or glass having ahigher coefficient of elasticity than the sheet 41 stacked on the sheet41. Since the sheet 44 having a higher coefficient of elasticity isstacked on the sheet 41, the movable element 4 has high rigidity. Thisenables the movable element 4 to be formed flatter, whereby the distancebetween the movable element 4 and driving electrodes 2 can be madeuniform. As a result, the force of driving the movable element 4 can beincreased.

FIG. 4 is a sectional view illustrating another example of the sheet 41.In the sheet shown in FIG. 4, portions 46 thereof are subjected to anelectret-forming process. In the example of FIG. 4, the portions 46 areprovided at regular intervals. However, they may be provided atdifferent intervals.

The structure of the movable element 4 shown in FIG. 4, in which theintervals of the portions 46 correspond to those of the drivingelectrodes 2, can receive a stronger force for driving the movableelement 4, than the structure in which the entire surface of the movableelement is subjected to an electret-forming process.

Referring then to FIG. 5, the stationary plate 1 will be described. FIG.5 is a sectional view illustrating a structure example of the stationaryplate 1 and driving electrodes 2. As shown in FIG. 5, a plurality ofdriving electrodes 2 are provided on the stationary plate 1. The surfaceof the stationary plate 1 that is provided with the driving electrodes 2is coated with an insulation layer 11. In the example of FIG. 5, thestationary plate 1 is formed of glass, the driving electrodes 2 areformed of aluminum, and the insulation layer 11 is formed of a siliconoxide sheet. The insulation layer 11 covering the stationary plate 1electrically isolates the adjacent driving electrodes from each other,thereby enabling an electrostatic force to be efficiently exerted on themovable element 4.

It is not always necessary to arrange the driving electrodes at regularintervals as shown in FIG. 5. It is sufficient if the electrodes canapply a sufficient electrostatic force to the electret-formed portionsof the movable element 4.

Referring now to FIGS. 6A to 6D, the operation principle of the shutterdevice of the first embodiment will be described. In the movable element4 shown in FIGS. 6A to 6D, portions arranged at regular intervals areelectret-formed portions as in the case of FIG. 4. That is, a pluralityof electret-formed portions 46 are provided at regular intervals in asheet 45. The electret-formed portions 46 are charged so that thesurface opposing driving electrodes 2 is negatively charged. Further,the driving electrodes 2 are connected to a drive control circuit 3, anda voltage is applied to the driving electrodes 2 by the drive controlcircuit 3. It is assumed in the shown example that the drive controlcircuit 3 is a 3-phase power supply circuit. However, the drive controlcircuit is not limited to this.

In the state shown in FIG. 6A, assume that the drive control circuit 3applies a positive voltage in the first phase (it is assumed that theleftmost is the first phase), and a negative voltage in the second andthird phases. At this time, the driving electrodes 2, in the firstphase, and the movable element 4 are charged with electricity ofopposite polarity, therefore they attract each other. On the other hand,the driving electrodes 2, in the second and third phases, and themovable element 4 are charged with electricity of the same polarity,therefore they repel each other. As a result, the movable element 4moves to the position shown in FIG. 6B. In the state of FIG. 6B, if anegative voltage is applied in the first and third phases, and apositive voltage is applied in the second phase, the movable element 4moves to the position shown in FIG. 6C. In the state of FIG. 6C, if anegative voltage is applied in the first and second phases, and apositive voltage is applied by the third phase, the movable element 4moves to the position shown in FIG. 6D. Thus, if a positive voltage isapplied in the order of the first, second and third phases, the movableelement 4 moves from right to left in the figures. If, on the otherhand, a positive voltage is applied in the order of the third, secondand first phases, the movable element 4 moves from left to right in thefigures.

By moving the movable element 4 as a light-shielding sheet as shown inFIGS. 6A to 6D, the shutter is opened and closed. Since a constantcharge exists at the surface of the movable element 4, a strongerdriving force can be acquired from a low voltage than in the case of ainduction electrostatic actuator.

FIG. 7 illustrates a voltage pattern example applied to drive themovable element 4. In FIG. 7, the abscissa indicates time and theordinate indicates the voltage applied to the driving electrodes 2. Inthe example of FIG. 7, the voltage applied to the driving electrodes 2is a rectangular wave voltage.

As shown in FIG. 7, in the first embodiment, in the range from timepoint 0 (the drive start time of the movable element 4) to time pointt₀, the frequency of the voltage applied to the driving electrodes 2 isincreased with time. From time point t₀, the frequency of the voltage iskept constant.

The application of the voltage to the driving electrodes 2 prevents themovable element 4 from being insufficiently accelerated at the start ofmovement of the element, and hence being unable to reach the position atwhich it can be attracted by the next driving electrode 2. If the pitchand/or width of the driving electrodes 2 is set as shown in FIGS. 8A to8C, the same advantage can be acquired even if a voltage of the patternshown in FIG. 7 is not applied thereto. FIG. 8A shows a case where thepitch P₀ of the driving electrodes 2 in the area (start area) in whichthe movable element 4 is moved from time point 0 to time point t₀ is setnarrower than the pitch P₁ of the driving electrodes 2 in the otherarea. Further, FIG. 8B shows a case where the pitch P₀ in the start areais set narrower than the pitch P₁ in the other area, and the width W₀ ofthe driving elements 2 in the start area is set narrower than the widthW₁ in the other area. FIG. 8C shows a case where the pitch and width ofthe driving elements in the start area are gradually increased towardthe other area (i.e., toward the right in the figure).

FIG. 9 is a flowchart useful in explaining control performed by thedrive control circuit 3 upon turn-on of the power supply. Upon turn-onof the power supply, the drive control circuit 3 performs voltageapplication to move the movable element 4 to a predetermined position(step S1). Subsequently, the drive control circuit 3 determines whetherthe movable element 4 is in the predetermined position (step S2). If itis determined that the movable element 4 is not in the predeterminedposition, the drive control circuit 3 returns the process to step S1where the movable element 4 is again moved. On the other hand, if it isdetermined that the movable element 4 is in the predetermined position,the drive control circuit 3 waits for an instruction to move the movableelement 4.

The determination at the step S1 is performed using, for example, acapacitance sensing circuit. The capacitance sensing circuit isconnected to one of the drive electrodes as shown in FIG. 10A. That is,the capacitance sensing circuit 6 shown in FIG. 10A is connected to thedrive control circuit 3 and the driving electrode that is located at theend of the stationary plate 1, i.e., a driving electrode 21. FIG. 10Ashows the positional relationship between the stationary plate 1 andmovable element 4, assumed when the power supply is off. After turn-onof the power supply, the drive control circuit 3 performs control formoving the movable element 4 to the position (i.e., the predeterminedposition mentioned in the flowchart of FIG. 9) corresponding to thedriving electrode 21 connected to the capacitance sensing circuit 6, asdescribed with reference to FIG. 9.

FIG. 10B shows a state in which the movable element 4 reaches thedriving electrode 21. When the movable element 4 reaches the drivingelectrode 21, the capacitance of the capacitor formed of the drivingelectrode 21 and movable element 4 significantly varies. The variationin capacitance is detected by the capacitance sensing circuit 6. As aresult, the drive control circuit 3 determines that the movable element4 has moved to the predetermined position, and stops the movable element4.

The control accuracy and driving efficiency of the movable element 4 areenhanced by always moving, to the predetermined position upon turn-on ofthe power supply, the movable element 4 whose position is not fixed whenthe power supply is off.

It is preferable to seal the movable element 4 of the shutter device 100as shown in FIG. 11. FIG. 11 shows an example in which the movableelement 4 is completely sealed with the stationary plate 1, protectionmember 51 and seal member 52. The protection member 51 is, for example,a glass thin plate, and the seal member 52 is formed of silicon. In thisstate, the movable element 4 is protected from temperature, humidity,dust, etc. As a result, the constant charge held in a sheet subjected toan electret-forming process is prevented from being attenuated bytemperature, humidity, dust, etc. In the example of FIG. 11, the drivingelectrodes 2 are also sealed, therefore they can also be protected fromperformance degradation.

Second Embodiment

A second embodiment of the invention will now be described. The secondembodiment is directed to a thin focal plane shutter device capable ofperforming shutter driving with low voltage at high speed, which is anapplication of the shutter device of the first embodiment.

In the case of, for example, an in-lens shutter mechanism, it must belocated at the position of a diaphragm. Since the position of thediaphragm is moved when, for example, the lens is focused, a mechanismfor moving the entire shutter mechanism is indispensable. This makes itdifficult to reduce the size of the in-lens shutter mechanism. On theother hand, in the case of a focal plane shutter mechanism, it islocated immediately before an image pickup element, therefore it is notnecessary to move the shutter mechanism even when, for example, the lensis focused. Therefore, it is not necessary to employ a mechanism formoving the shutter mechanism, which enables the shutter mechanism to bereduced in size.

FIG. 12 shows a focal plane shutter that comprises a shutter device 101formed of a stationary plate 1 with an opening 5 and a movable element4, and a shutter device 102 formed of a stationary plate 19 and movableelement 49 and having the same structure as the shutter device 101. InFIG. 12, if, for example, the movable elements 49 and 4 are used asfront and rear curtains, respectively, a focal plane shutter to bedriven at high speed with low voltage is realized. Further, FIG. 12shows a state in which the front and rear curtains are both open. It isdesirable that the driving voltage applied to the driving electrodes 2on the stationary plate 19 should have the same phase as that of thedriving voltage applied to the driving electrodes 2 on the stationaryplate 1. If the driving voltages are made to have the same phase, unevenexposure can be avoided.

Various modifications as explained in the first embodiment can also beemployed in the focal plane shutter shown in FIG. 12. In addition,so-called direct metering, in which metering is performed using lightreflected from the front curtain of a focal plane shutter, may be usedas a metering scheme for a camera having a focal plane shutter. Thefocal plane shutter of the second embodiment may be constructed to becompatible with such direct metering. In this case, it is sufficient ifthe front curtain 49 has a predetermined pattern that provides astandard reflectance.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A shutter device comprising: a first shutter unit including a firststationary plate with a plurality of driving electrodes arranged with afirst predetermined pitch, and a first movable element opposing thefirst stationary plate, the first movable element including a sheetsubjected to an electret-forming process; and a second shutter unitincluding a second stationary plate with a plurality of drivingelectrodes arranged with a second predetermined pitch, and a secondmovable element opposing the second stationary plate, the second movableelement including a sheet subjected to an electret-forming process, andwherein the plurality of driving electrodes arranged with the first andsecond predetermined pitches are arranged on the first and secondstationary plates with a first pitch in a start area ranging from aposition at which the first and second moveable elements start to move,to a predetermined position, and with a second pitch in an area otherthan the start area; and a pitch of the first pitch interval in thestart area is narrower than a pitch of the second pitch interval whichis in an area other than the start area.
 2. The shutter device accordingto claim 1, wherein the plurality of driving electrodes arranged withthe first and second predetermined pitch on the first and secondstationary plate have a first width in the start area, and have a secondwidth wider than the first width in the area other than the start area.3. The shutter device according to claim 2, further comprising a drivecontrol unit configured to drive the front curtain and the rear curtainat an identical phase.
 4. The shutter device according to claim 2,wherein at least the first movable element and the second movableelement are sealed with a seal member.